The invention relates to monitoring units in tilting systems used in railway vehicles to control longitudinal roll motion mechanisms in order to increase passenger comfort. In particular, knowing the speed, the lateral acceleration and the tilting angle command from the tilting system, the invention enforces the comfortable operation of a train tilting system.
It is becoming necessary to rethink the actual train infrastructure: travel time must be reduced to compete with airlines, existing tracks must be shared with freight trains, and land or budget constraints often prohibit the construction of dedicated high-speed tracks. The only solution is tilt technology. The need for tilting control systems was discussed in the November 1996 issue of Popular Mechanics magazine, in an article entitled xe2x80x9cAmerican Flyerxe2x80x9d, as being a solution to improve passenger comfort during train rides. High-speed tilting trains require finely tuned mechanisms to ensure passenger comfort.
A xe2x80x9ctilting systemxe2x80x9d is a combination of electrical, electronic and hydraulic components that control a railway car""s longitudinal roll motion mechanism. It is used in passenger trains in order to increase passenger comfort that is affected by centrifugal acceleration in curves. Centrifugal acceleration is a serious limiting factor to the maximum cruising speed of a passenger train.
The maximum speed allowed in curves is limited by three factors: the maximum tilt angle of the car (usually between 5xc2x0 and 9xc2x0), the maximum steady state residual lateral acceleration and the forces applied to the tracks by the non-tilting locomotive, which is almost two times heavier than a passenger car. The dynamic wheel/rail forces are almost identical for both a tilting and a non-tilting car at a given speed. All forces vary with the square of the speed.
Railroad curves are generally designed in order to compensate for a portion of the centrifugal acceleration by means of track super-elevation (or cant angle) that will force the car body to tilt along its roll axis. Properly oriented this tilt angle creates a gravitational component vector reducing the centrifugal force felt by the passengers in curves. The maximum super-elevation angle is typically 6xc2x0. On conventional tracks, the presence of heavy freight trains is one source of limitation for the maximal super-elevation. There is a maximal force that the inner rail can tolerate when the heaviest vehicle allowed to roll on The said track is immobilized in the curve.
Considering this design criteria, one can demonstrate that most passenger railway corridors in North America and Europe presently lack the proper amount of curve super-elevation that would allow the operation of high-speed trains without seriously compromising passenger comfort. Since modifications to conventional tracks are too costly and since speed and passenger comfort are the key to the survival of the passenger train industry, the solution resides in tilting systems.
Passenger cars equipped with an active roll motion mechanism, also called a xe2x80x9ctilting systemxe2x80x9d can overcome this cant deficiency problem by giving the proper amount of roll to the car body in order to compensate for the lack of curve super-elevation. Passenger comfort is then improved and high-speed operation becomes possible on most existing railway corridors.
Tilting the body of a rail passenger car during curve negotiation offers the possibility of increasing the speed of a trainset in a curve without exceeding the maximum allowed steady state lateral acceleration felt by the passengers. Typically, the lateral acceleration due to centrifugal force should be lower than 1 m/sec2 (i.e. lower than 0.1 g). This tilting feature reduces the overall traveling time without requiring track modification. Moreover, an effective tilting system greatly improves the passenger ride comfort during curve entry and exit by minimizing the transient accelerations.
Usually, the tilting mechanism only cancels 70% of the centrifugal force. A March 1993 article in Popular Mechanics magazine entitled xe2x80x9cBullet Train for Americaxe2x80x9d explains the effect of the tilting system on the passenger: xe2x80x9cStanding up, a rider notices the floor push gently against the left foot, as the view out the window pitches skywardxe2x80x9d. The reason why the centrifugal acceleration is not compensated 100% is because neural signals from the eye would clash with those from the inner ear of the passengers, which senses no change at all and would cause motion sickness.
The tilting system is activated by the locomotive engineer before the train undertakes a run. A cab indicator informs the engineer of the tilting system status. When the system is activated, the locomotive engineer can operate the train at higher speeds. If the tilting system is deactivated, the train engineer must return to conventional speed in all curves for passenger comfort purposes. The difference between tilting and conventional speeds in high-speed curves is typically 35 km/h.
When passengers travel on such tilting trains, their comfort must be guaranteed at all times. The consequences of a failure to compensate the lateral acceleration correctly are immediate. Miscalculations of the proper compensation or erroneous actuation could result in increased motion sickness felt at the passenger level and, potentially, lost of balance. The generation of a tilt angle command must handle the worst-case scenario and, in addition, means to cancel the tilting command must be provided.
Tilting of the car is accomplished by a servo-valve controlling the hydraulic mechanism, which in turn tilts the car. The tilting control system responds to the output of a low-pass filtered inertial sensing system. Within a curve, cant deficiency is stable and passengers experience the cant improved by the tilting system. But delays introduced by the low-pass filtering could lead the passengers to experience a discomfort twice in a curve: at entry and exit. At these locations, the outward acceleration felt by the passengers is compounded by the acceleration of the tilt system, i.e. the outward acceleration due to the curve is added to the outward acceleration due to the roll movement of the compensating tilting. The reaction time and the accuracy of the control system are therefore critical. It is important for the control system to notice malfunctions and react rapidly and adequately.
If the tilting system is not closely monitored, various degrees of uncomfortable situations can occur, including passenger loss of balance and beverage spilling.
Similar uncomfortable situations would also occur when trains tilt in straight track segments.
It is the object of the present invention to provide a method which dynamically adjusts the threshold (or acceptable limit) value for the detection of malfunctions. The decision to generate an alarm signal will automatically arise as a function of the input signal polarities and absolute values. According to a further object of the present invention, passenger comfort will be increased since detection of abnormal operation of the tilting system will be performed rapidly. Finally, one further object of the present invention is to provide a method and system which dynamically adjust the threshold value to measure the performance of the tilting system.
The present invention is directed to a method that satisfies the need for an early detection of faulty tilting control system behavior due to failures. It allows fast and reliable shutdown capability of a malfunctioning tilting control system.
A failure in a part of the tilting system, which can lead to passenger discomfort, can be identified when one of the following is detected:
1) There is an inverse tilting command in a curve requiring tilting, i.e. the train tilts on the wrong side;
2) There is a tilting command in a straight (tangent) track segment, i.e. the train is going in a straight line but is tilting; and
3) The tilting command in a curve is properly oriented, but not sufficient to meet comfort criteria, i.e. the cant angle is too small and the train does not tilt enough.
The occurrence of case 1 or 2 denotes an important malfunction of the tilting system, which could greatly affect passenger comfort. Therefore, the detection of these conditions shall be performed according to stringent requirements.
On the other hand, since some amount of residual lateral acceleration in a curve is expected for passenger comfort, the occurrence of case 3 could be caused, for example, by a wrong control parameter adjustment, e.g. the ratio of cant deficiency compensation. In this case, the acceptable residual acceleration criterion is different than in cases 1 and 2. An over-speed situation in a curve could also lead to case 3, since there is a limit to the maximum tilting angle achievable.
In order to detect a situation where passenger comfort could be affected, an accelerometer can be installed on the passenger car floor level to measure lateral acceleration, which can be compared to a static threshold value. In this case, the threshold would have to be adjusted to a small value in order to obtain a prompt detection for cases 1 and 2. However, the value of this threshold could be too restrictive for normal tilt operation, and would cause false anomalous detection.
To generate an alarm when malfunctions or poor performance occur in a train tilting system, according to one broad aspect of the invention, the lateral acceleration to which passengers are subjected in a passenger car is measured. It is compared to an acceptable level of lateral acceleration and this comparison alters the control of the tilting system. This altering can be a trigger for a cab indication, a means for shutting down the tilting system or another alarm output system. This monitoring can be done on a car-by-car basis.
According to a preferred feature of the invention, the polarities of the lateral acceleration of a passenger car and the tilting command for that passenger car are compared to determine a polarity check flag. Using this polarity check flag, the absolute value of the tilting command, the train speed and the polarity of the lateral acceleration, a lateral acceleration limit is produced. This lateral acceleration limit can be one of four limit lines, a constant value, a function of speed or chosen via a comparison table. If the lateral acceleration is greater than the lateral acceleration limit for a pre-determined period of time, an alarm is produced.
According to another broad aspect of the invention, a system for monitoring malfunctions is composed of means to measure the lateral acceleration, a comparator for comparing the lateral acceleration with a limit for the lateral acceleration and means to alter the control of the tilting system. According to another preferred feature of the invention, a system for monitoring malfunctions is composed of two polarity detectors, an absolute value detector, a comparator for the polarities of the lateral acceleration and the tilting command, a threshold function that generates the limit for the lateral acceleration, another comparator for comparing the lateral acceleration with the limit and a persistency check that outputs an alarm if the tilting system is malfunctioning for a period of time longer than a pre-determined delay.